1. Field of the Invention
An object of the present invention is a universal-purpose, tunnel type convertible gamma camera preferably with two rings. The aim of the invention is to make the design of such a gamma camera more rational so that it can be used for a plurality of purposes.
Gamma cameras of the PET and SPECT (positron emission tomography, and single-photon emission computer tomography) are known in the field of nuclear medicine. In the former case, they have to detect the appearance of phenomena of nuclear emission in coincidence on two opposite and facing detectors. In the latter case, they are used to detect nuclear emissions sent in at least one direction. The invention can be applied to either of these two techniques.
The principle of these phenomena is as follows. A radiological marker is injected into a body to be examined, for example a patient""s body. This marker is more generally technetium, and sometimes thallium, or another marker. Depending on a metabolic charge, the markers will get fixed preferably in certain organs of a patient""s body. Through the density of this fixation, they reveal the functional state of the organ in which they get fixed. These markers emit camera rays during their metabolization. These gamma rays are detected by a detector.
A detector of this kind has a collimator on an input face. The role of this collimator is to acquire an image in projection. However, there are known ways of having collimators with inclined holes or focused holes. The gamma rays that cross the collimator then reach a scintillator whose role is to convert each gamma ray into a light scintillation. This light scintillation is detectable by a set of photomultiplier tubes placed downline from the scintillator. The photomultiplier tubes detect the scintillations and deliver corresponding electrical signals whose amplitude and shape reveal the nature and position of the nuclear event detected. These signals are processed, especially in barycenter-determining matrices, to constitute an image revealing this nuclear activity.
2. Description of the Related Art
Several types of examinations are performed. There are especially, on the one hand, tomography operations and, on the other hand, whole-body images. In one tomography operation, a projected image is acquired for a given incidence of the detector with respect to the patient""s body. Then another projected image is acquired for another incidence, offset by some degrees with respect to the former. Continuing progressively in this way, a great many projected images are acquired. From these images, through the use of image reconstruction algorithms (of the same type as those used in tomodensitometry) a 3D image is acquired of the organ being studied. The projected images are acquired slowly. Typically, the period of acquisition of a projected image oscillates between 5 seconds for the fastest ones, up to 2 minutes for the finer images. In the European patent application EP-A-0 517 600, it has been explained that, to accelerate image acquisition in tomography, it is preferable to use two detectors, and also to place these detectors at 90xc2x0 to each other around the patient""s body.
Another examination relates to so-called whole-body images. To acquire an image of this kind, the detector is moved in translation along the patient""s body while he or she is supine. This type of examination is used to take essentially an angiographic image of the patient""s legs, especially to detect problems of vascular insufficiency. Preferably, also in this case, to increase image quality, a second detector is placed beneath the patient""s body. The patient then gets translated between these two detectors. With certain machines, the patient is immobile and the machine moves with respect to him or her.
Other examinations are practiced such as cardiography with exertion. For these other examinations, the patient is subjected to physical exertion at the same time as the images are taken.
The different types of images made require that the detectors should be highly mobile with respect to one another. The machines designed to carry them out efficiently are machines of two types: tunnel machines or open-gantry machines, that is machines with arms. In a tunnel machine, the patient goes into a tunnel whose walls mechanically support the detectors. In a machine with arms, a gantry holds two arms each supporting a detector, the patient being presented between these arms. There is the known exemplary patent application PCT/US95/13180 in which there is a combined machine with both a tunnel and arms. The problem presented by these different machines is that they are complicated to manufacture. Indeed, the detection technology, especially that of collimators, requires heavy detectors. In practice, the weight of these detectors may be in the range of 300 or 400 kilos. Given the different ways of positioning these detectors around the patient""s body and the required precision of about 1 millimeter each time, the gantries that bear these machines are massive. They are all the more massive as, in the hospitals and medical centers in which they are installed, the floor on which they rest is often not perfect. In these cases, these gantries must be capable of coping with these problems of the floor.
Besides, to go from a tomography type of examination to a whole-body type of examination, the tunnel machines and the machines with arms have different advantages and drawbacks. In the tunnel machine, it is enough to make the patient""s bed go through the tunnel. In a machine with arms, the bed that supports the patient must be rotated by 90xc2x0 with respect to the machine before the whole-body examination can be made. This drawback however is compensated for with this machine in that it enables the use of the patient""s hospital bed instead of the examination bed. For patients who are bed-ridden or cannot be carried out of their beds, it is enough to replace the bed of the machine with the patient""s bed.
For various reasons, however, tunnel machines are preferred.
One problem to be resolved therefore is that of designing a tunnel machine that can be used to perform angiography on patients when these patients are left in their hospital bed and when they are not lying on the examination bed. This problem is partially resolved by the combined machine referred to here above. However, it is costly to design since it includes all the mechanisms of the two machines. Furthermore, for examinations during which the patient is sitting or facing the machine, or else doing a work-out in an exertion machine, the frontal presentation of the detectors proposed by this machine makes these examinations impractical to perform. The space taken up by the underframe of this combined machine as well as the presence of the patient""s own bed are a hindrance to these examinations.
In the invention, this problem is resolved by choosing a tunnel machine. This tunnel machine however is not a complicated one. The problem of complexity is resolved therein by fitting out a support of a detector with a folding arm. The folding arm or flap can thus take two preferred positions. A first position of the flap in this support presents the detector so that it faces the tunnel of the machine. In this position, it is possible to carry out both tomography and whole-body examinations. These whole-body examinations are then made on patients likely to get placed in the machine bed. In the other position, a single detector is transferred by the folding arm. It is transferred to the side of the machine. Then, parallel to this tunnel of the machine, there is far more space available to place an examination chair, an exertion machine or a bed for a patient who cannot be transferred.
In this case, in the invention, these examinations will be made with only one detector. Therefore, to obtain adequate image quality, the shooting time for each image must be sufficiently long. However, this does not entail any penalties since these examinations are relatively infrequent and, from this point of view, the invention achieves an efficient compromise between the cost of the machine and its real efficiency. Furthermore, the system of folding the arm is very simple. Consequently, it does not give rise to any major additional cost.
An object of the invention therefore is a tunnel type gamma camera with at least one ring rotating about an axis of rotation passing into a tunnel, this ring bearing a detector by means of a support, wherein the support has a folding arm mechanically linked firstly to the ring and secondly to the detector, this arm being provided with a hinge with an axis offset with respect to the detector and being capable of occupying at least two angular positions with respect to this offset axis, a first angular position enabling the detector that it carries to be presented so that it faces the tunnel, and a second angular position enabling it to be presented beside the tunnel.